Heat storage composition, latent heat storage capsules containing said heat-storage composition and temperature control apparatus using said capsules

ABSTRACT

A heat storage composition excellent in heat storing effect contains calcium chloride hexahydrate as the main component and an appropriate amount of a nucleating agent combination for inhibiting supercooling which is composed of barium sulfide, barium chloride dihydrate and strontium chloride hexahydrate or of barium chloride dihydrate and strontium chloride hexahydrate and optionally contains an appropriate amount of a thickening agent combination composed of an ultrafine silica powder and glycerin. Latent heat storage capsules contain the above heat storage composition and are improved particularly in their structure such that improved heat storage and release effects can be produced. A temperature control apparatus can make most of the heat storage capsules in the temperature control of a hothouse or the like.

This is a division of application Ser. No. 850,100, filed Apr. 10, 1986,now U.S. Pat. No. 4,715,978, granted Dec. 29, 1987.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a heat storage composition for use ingreenhouses for facility horticulture or cultivation, in living areaheating, in chemical heat pumps, further in solar energy storage tanksand industrial waste heat recovery facilities, and in other fields, tolatent heat storage capsules improved such that the heat-storage andrelease characteristics of said heat-storage composition can be utilizedto the possible maximal extent, and to a temperature control apparatusin which said capsules are used efficiently in temperature control invarious hothouses and the like.

2. Background Art

Calcium chloride hexahydrate has a solidification point of about 30° C.,which is close to the ordinary temperature range, with a great latentheat of solidification/melting which is characteristic of a hydrate, andtherefore is coming into wide and practical use in greenhouses forfacility horticulture and plant cultivation, in living area heating, inchemical heat pumps, further in solar energy storage tanks andindustrial waste heat utilization facilities, among others. However,this compound involves a serious problem that a marked supercoolingphenomenon is observed with it. This is an obstacle to practical use ofsaid compound. The phenomenon of supercooling is a phenomenon that theliquid-to-solid phase change does not begin in the process of cooling ofa substance in the liquid phase even after passage of the solidificationpoint but at last begins at a temperature considerably below thesolidification point. When supercooling takes place, the solidificationpoint at which the latent heat of solidification should be releasedbecomes unspecified and this is a fatal defect in the use as a heatstorage material for maintaining a specific temperature range. Forsolving such problem, a technique of preventing supercooling has beenproposed (e.g. Japanese Patent Publication No. 32749/80 and No. 9059/81)which comprises adding to calcium chloride hexahydrate a nucleatingagent capable of promoting crystallization thereof. Said technique isunder development for early practical use. Many substances are known asnucleating agents for such use, for example, strontium chloridehexahydrate, strontium hydroxide octahydrate, strontium oxide, bariumhydroxide octahydrate, barium carbonate and barium nitrate. Addition ofthese in an amount of 0.1-20 percent by weight on the whole heat-storagecomposition basis can prevent the supercooling of calcium chloridehexahydrate to a considerable extent.

However, check experiments made by the present inventors for evaluatingthe effects of various nucleating agents have revealed that anynucleating agent cannot prevent the occurrence of supercooling by about3°-4° C. Moreover, addition of more than 20 percent by weight of anucleating agent cannot be expected to produce any further effect.

On the other hand, when calcium chloride hexahydrate is used alone, thelatent heat release temperature is specifically restricted to one singlepoint, namely about 30° C. which is the solidification point (and at thesame time the melting point) thereof, so that it is difficult to adjustthe same to the use conditions with respect to said temperature.Therefore, the latent heat release temperature is generally adjusted byaddition of a solidification point adjusting agent such as FeCl₃.6H₂ O,MgCl₂.6H₂ O or CoCl₂.6H₂ O. However, the nucleation-promoting agents andsolidification point modifiers, when used alone in heat-storagecompositions, gradually lose their effects upon repeated use as a resultof precipitation thereof in the heat-storage material-containing vesselsand eventually their effects cannot be fully produced any more in someinstances. It is also known that upon repeated liquid-solid phasechanges, calcium chloride hexahydrate itself gradually precipitates onthe vessel bottom due to a specific gravity difference between theliquid phase (having a specific gravity of 1.5) and the solid phase(having a specific gravity of 1.68), leading to phase separation.

Therefore, for the purpose of increasing the dispersion stability ofadditives including nucleation-promoting agents and preventing phaseseparation, a thickening agent is added to heat-storage compositions.The thickening agent is used to achieve the above purpose by providing amelt under use with an appropriate viscosity and includes, among others,alcohols, such as glycerin and ethylene glycol, carboxymethylcelluloseand poly(sodium acrylate).

Among the above thickening agents, glycerin is particularly valuablesince it is miscible with water in any proportion, is capable ofproviding an adequate viscosity and has good stability. However, sincesaid substance has solidification point depressing activity, greatvariations in solidification point are inevitable even when it is usedfor the purpose of viscosity increase, particularly when it is used inrelatively large amounts so as to attain high viscosity values. On theother hand, the use of those thickeners which are so far in general use,for example high-molecular substances such as poly(sodium acrylate) isdisadvantageous in that although they have excellent viscosityincreasing effects, repeated use thereof results in local caking andviscosity reduction and eventually in failure in its duty to producehomogeneous dispersion.

Failure in dispersion of the nucleating agent and other auxiliaryingredients leads to substantial failure in answering the intendedpurpose of their incorporation, namely loss of their ability to preventthe phenomenon of supercooling on the occasion of phase transition, andat the same time allows phase separation, whereby the value of theheat-storage material containing them is reduced.

Meanwhile, the use of latent heat-storage capsules with a latentheat-storage material capable of thermal phase change, namely aphase-change material, sealed therein (hereinafter, "PCM capsules") asheat sources for various purposes has been proposed, for example forstoring solar energy therein for later heat radiation for heatingpurposes or, more broadly, for storing solar energy in summer foremission in winter for various heating purposes. Such PCM capsules areunder way for practical use.

As the above-mentioned PCM capsules, there are known spherical ones(e.g. Japanese Utility Model Application No. 109283/83) and flat ones(e.g. Japanese Utility Model Application No. 105796/84), among others.From the viewpoints of ease in placing, ease in forced circulation of aheat transfer medium in heat exchange, and so forth, the latter flat PCMcapsules may be said to be more advantageous.

In particular, for heat exchange between PCM capsules and air as a heattransfer medium, flat PCM capsules are preferable.

However, flat PCM capsules are very small in thickness as compared withthe other dimensions, length and breadth, so that when they are in thevertical disposition, the latent heat-storage material, for examplecrystalline calcium chloride (CaCl₂.6H₂ O), or a nucleating agenttherefor contained in the flat PCM capsules precipitates on thecontainer bottom, whereupon the crystal growth owing to the nucleatingagent, namely the phase change of the latent heat-storage material,cannot be promoted in a uniform manner any more, hence,disadvantageously, the heat-storage effect cannot be produced to asatisfactory extent.

It is conceivable that horizontal disposition of flat PCM capsules mightsolve such problem.

In that case, the nucleating agent is dispersed uniformly and generallyover the flat bottom portion of the flat PCM capsules and this favorablycauses uniform phase change in the latent heat-storage material.However, when the temperature of the flat PCM capsules is lower thanthat of air and thus there is a temperature difference from the air inthe stage of heat storing, dew condensation can easily occur on the flatPCM capsule surface. The water resulting from this dew condensation canhardly be discharged and moreover that portion of heat which is consumedfor the vaporization of this water is directly reflected in adisadvantageously reduced heat-storage efficiency.

Furthermore, in using PCM capsules in temperature control apparatus foruse in various hothouses and the like, it is necessary to provide aseparate heating unit in addition to the PCM capsules so that theshortage of heat as resulting from insufficient heating, for example inwinter when the duration of sunshine is short, can be filled up. Whensuch a heating unit is used combinedly, heat radiation from said unitcan hardly extend over the whole hothouse and this readily results inlack of uniformity in temperature within the hothouse. For avoiding suchtrouble, a blower is required for circulating the air within thehothouse to thereby cause the heat radiated extend over the wholehothouse.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings,

FIG. 1 graphically represents an example of the supercooling curve forthe heat storage composition;

FIG. 2 is a plan view illustrating an example of the heat storagecapsule according to the invention;

FIG. 3 is a cross-sectional view of said example as seen along the lineIII--III in FIG. 2;

FIG. 4 shows enlarged partial cross-sectional views of said example,FIG. 4A along the line A--A, FIG. 4B along the line B--B, and FIG. 4Calong the line C--C in FIG. 2;

FIG. 5 illustrates the condition in which heat storage capsulesaccording to the invention are used;

FIG. 6 is a cross-sectional front view showing an example of thetemperature control apparatus according to the invention;

FIG. 7 is a cross-sectional side view of the apparatus shown in FIG. 6;

FIG. 8 is a cross-sectional view of the same apparatus as seen along theline VIII--VIII in FIG. 7;

FIG. 9 illustrates the condition in which the temperature controlapparatus shown in FIGS. 6-8 is used;

FIG. 10 is a cross-sectional front view of another example of thetemperature control apparatus;

FIG. 11 is a cross-sectional side view of a further example of thetemperature control apparatus;

FIGS. 12-21 each is a graphical representation of the degree ofsupercooling in a heat storage composition according to the invention;

FIG. 22 is a graphical representation of the relationship between thelevel of addition of a solidification point modifier and thesolidification points;

FIG. 23 is a graphical representation of the relationship between thelevel of addition of a solidification point modifier and the quantity ofheat stored;

FIG. 24 is a graphical representation of the relationship between thelevel of addition of an ultrafine silica powder or glycerin and theviscosity of the heat storage composition in the molten state;

FIG. 25 is a graphical representation of the influence of the level ofaddition of an ultrafine silica powder and of glycerin on the viscosityof the heat storage composition in the molten state;

FIG. 26 is a graphical representation of the relationship between thenumber of melting-solidification cycles and the degree of supercoolingfor an example of the heat storage composition according to theinvention;

FIGS. 27-30 each is a cross-sectional elevation view of a furtherexample of the heat storage capsule according to the invention;

FIG. 31 is a schematic view in section which illustrates a technology ofmanufacturing the heat storage capsule shown in FIG. 30;

FIGS. 32A and 32B are enlarged partial cross-sectional views whichschematically illustrate a fit-fusion technique as applied to the inletafter heat storage composition charging; and

FIGS. 33A and 33B are enlarged partial cross-sectional views whichschematically illustrate another fit-fusion technique as applied to theinlet after charging of a heat storage composition.

DETAILED DESCRIPTION OF THE INVENTION

An object of the invention, which has been worked out to solve theproblems involved in the prior art as mentioned above, is to provide aheat storage composition which consists mainly of calcium chloridehexahydrate and is capable of substantially avoiding the phenomenon ofsupercooling and absorbing or releasing the latent heat ofsolidification with certainty at a temperature around the theoreticalsolidification point. Another object of the invention is to provide aheat storage composition which is highly stable with respect to phaseseparation among the elements constituting the heat storage composition,i.e. main constituent (calcium chloride hexahydrate), nucleating agent(barium sulfide, etc.), solidification point modifier (zinc chloride,etc.) and so on, and can produce a high-level heat storage effect evenin repeated use thereof. A further object of the invention is to providea flat PCM capsule which contains the above heat storage composition inthe sealed state, has an improved structure and makes it possible forthe heat storage/release characteristics of the heat storage compositionto be utilized efficiently. A still another object is to provide atemperature control apparatus in which said PCM capsule can be made themost of for temperature control in various hothouses and the like.

Such objects of the invention have been accomplished by providing theconstitutions specified in the accompanying claims.

When a heat storage composition consisting substantially of calciumchloride hexahydrate alone is cooled from the molten state, it does notbegin to solidify even after passage across its solidification point(about 29.5° C.) but begins to solidify rapidly at about 20° C., forinstance, as indicated by the solid line in FIG. 1. The degree of suchsupercooling varies greatly depending on the rate of cooling and theextent of disturbance of the melt, among others, so that the temperatureat which the latent heat is released cannot be specified. Accordingly,the temperature control in response to a desired temperature cannot butbecome imprecise. When a nucleating agent for preventing supercooling,for example strontium chloride hexahydrate, is added to the compositionin an amount of about 5 percent by weight, the phenomenon ofsupercooling is much inhibited and the degree of supercooling is reducedto about 3°-4° C., as indicated by the broken line in FIG. 1. However,such supercooling inhibiting effect of known nucleating agents cannot besaid to be fully satisfactory although the optional addition leveldiffers only to some extent depending on the kind of the nucleatingagent. Thus, it is not that supercooling can be controlled substantiallywithin an acceptable range.

After a number of experiments with various compounds, the presentinventors confirmed that the phenomenon of supercooling can besuppressed very effectively by using barium sulfide and barium chloridedihydrate combinedly in certain specific amounts. It was further foundthat, as will be described later in the examples, the coexistence, in aheat storage composition containing calcium chloride hexahydrate as themain component, of 0.001-5 percent of barium sulfide and 0.05-5 percentof barium chloride dihydrate can suppress the supercooling to at most 2°C. When the amount of barium sulfide or barium chloride dihydrate islower than the lowest limit given above, the synergistic supercoolinginhibiting effect arising from their combined use cannot be expected anymore but only an incomplete supercooling inhibiting effect (supercoolingof about 5°-6° C.) as obtainable by their single use can be produced. Onthe other hand, when the contents of the above two additives exceed therespective upper limits, solidification does not occur in some instancesor the quantity of latent heat decreases greatly, so that theperformance and stability of the heat storage material deteriorate.

In a further study, it was found that when a small amount of strontiumchloride is used in combination with barium sulfide and barium chloridedihydrate, a satisfactory supercooling inhibiting effect can be securedeven at a further reduced total nucleating agent addition level. In viewof such excellent supercooling inhibiting effect of strontium chloridehexahydrate, it was expected that a satisfactory supercooling inhibitingeffect might be still obtained even when one of barium chloride orbarium sulfide is omitted, and investigations were conducted in thisdirection in an attempt to omit the use of barium sulfide which can be asource of hydrogen sulfide. As a result, it was found that asatisfactory supercooling inhibiting effect can be produced whenstrontium chloride hexahydrate and a slightly increased amount of bariumchloride are used combinedly. After determination of the optimumcontents of the above components, the present invention has now beencompleted.

Thus, in accordance with the invention, the contents of barium sulfideand the nucleating agents can be reduced to 0.0001-5 percent and 0.001-5percent, respectively by adding 0.001-0.1 percent of strontium chloridehexahydrate as an additional nucleating agent to the whole heat storagecomposition, as will be detailedly described later in the examples. Whenstrontium chloride hexahydrate is used in an amount of not less than0.06 percent the combined use of barium chloride dihydrate alone asanother nucleating agent in an amount of not less than 0.5 percent canproduce a satisfactory supercooling inhibiting effect. The supercoolinginhibiting effect is dependable and sufficient at very low nucleatingagent addition levels if the levels of addition of the nucleating agentsmeet the conditions given below.

Thus, the nucleating agent contents (or addition levels), X (%) forbarium sulfide, Y (%) for barium chloride dihydrate and Z (%) forstrontium chloride hexahydrate, which are preferred are as follows:

    0≦X≦5

    0.001≦Y≦5,

    0.001≦Z≦0.1, and

[I] when 0.06≦Z≦0.1, then

X=0 and Y≧0.5,

[II] when 0.005≦Z≦0.06, then

X≧0.0001 and Y≧0.01, or

[III] when 0.001≦Z≦0.005, then

X≧0.001 and Y≧0.01.

As mentioned above, a heat storage composition which will causesubstantially no supercooling phenomenon and has an optionally selectedlatent heat release temperature can be obtained by incorporating into aheat storage material mainly consisting of calcium chloride hexahydratea specific nucleating agent consisting of barium chloride and so on andfurther, optionally, a solidification point modifier, such as zincchloride, potassium bromide, sodium bromide or ammonium bromide. Uponrepeated use, namely after repetition of the solidification-meltingcycle, even this heat storage composition may sometimes deteriorate inits performance as a result of precipitation of part of said nucleatingagent or solidification point modifier as crystals. In such case,however, the dispersion stability of the whole heat storage compositioncan be markedly improved by incorporating into the heat storagecomposition an adequate amount of an ultrafine silica powder plusglycerin as a thickening agent. As said ultrafine silica powder, theremay be used a high purity ultrafine silica powder, such as Aerosil(trademark) of Degussa, West Germany. Supposedly, such substanceexhibits its thixotropic property owing to the action of the silanolgroup (.tbd.Si--OH) which said substance has in its structure. Saidsubstance occurs as very minute particles (7-40 μm) and is highlydispersible in various media. Thus, when incorporated into the heatstorage composition, said substance is dispersed uniformly whilemaintaining the fine particulate state. It is presumable that, uponmelting of said composition, particles of said substance are connectedwith one another by forming crosslinks and that, as a result, athickening effect is produced.

Ultrafine silica powders have so far been used as thickening agents forpaints or as sagging or running inhibitors for paints for thick coatingof walls, among others, and their thickening effect is well known.Hithertofore, however, there have been no instances of their use asthickening agents for heat storage compositions.

The present inventors have confirmed that ultrafine silica powdersproduce excellent thickening effect in heat storage compositions whichare in the molten state and are very stable both chemically andphysically and little susceptible to different heat storage compositionsor to environmental conditions, such as heat. Thus, addition inrelatively small amounts of an ultrafine silica powder as a thickeningagent together with glycerin to a heat storage composition whose maincomponent is an inorganic substance in a hydrate form and which mayoptionally contain a solidification point modifier and/or a nucleationpromoting agent gives a necessary and sufficient viscosity. Moreover, anultrafine silica powder does not aggregate or cake or otherwise degradeeven after repetition of the heat storage-release cycle. Furthermore,the addition of glycerin does not affect the solidification point sincea low level of addition of glycerin is already sufficient. Therefore,the heat storage composition with an ultrafine silica powder andglycerin incorporated therein as thickening agents exhibits excellentrepetition stability, reveals no ununiform dispersion or phaseseparation phenomenon, and can maintain a high level of dispersionstability for a prolonged period of time.

The flat PCM capsule according to the invention which has been improvedso that the characteristic features of the above heat storagecomposition can be utilized therein effectively and efficiently.

FIG. 2 is a plan view illustrating an example of the heat storagecapsule according to the invention; FIG. 3 is a cross-sectional view ofsaid example as seen along the line III--III in FIG. 2; and FIG. 4 showspartial cross-sectional views of said example, FIG. 4A along the lineA--A, FIG. 4B along the line B--B, and FIG. 4C along the line C--C inFIG. 2.

The flat PCM capsule 1 according to the invention comprises arectangular plate-like hollow vessel 10 generally formed by blowmolding. The vessel 10 has a plurality of oblong recesses 11, surroundedby slant faces 11B and 12B, as formed by bonding together by fusion thebottoms 11A and 12A at corresponding sites on both face plates 10A and10B (FIG. 3) and also a plurality of circular holes 13 formed by fusionbonding in the same manner as above to form circular recesses 12followed by punching at least at the fused bottom of said circularrecesses 12. The circular holes 13 thus pass through the hollow vesselin the thickness direction thereof. In the neighborhood of each of theleft and right edge portions 14A and 14B (as viewed on the drawing; thesame shall apply hereinafter) of each face plate, the hollow vessel hasat least one groove-like recess 15 continuously extending in thelongitudinal direction. In the neighborhood of each of the four corners14C--14C, there is provided a protrusion 16. The four protrusions 16 oneach face plate serve as spacers and are located at sites correspondingto the protrusions on the other face plate (FIG. 3). The vessel issealable after charging the hollow space 10C with a latent heat storagecomposition B₁ containing a nucleating agent B₂ etc.

In FIG. 2, 17 indicates an inlet for the latent heat storage compositionB₁. After charging, the inlet is hermetically closed by thermal fusionor stoppering.

In FIG. 2, 18--18 indicate compressed portions at the corners of theflat PCM capsule 10, which are to serve as fenders for preventingbreakage of the PCM capsule due to collision with some other body andalso to serve to avoid formation of narrow areas within the insidespace. On the drawing, the compressed portions 18 are found only at thebottom corners although such may be provided at all the four corners.

In practical use, plural units of this flat PCM capsule 1--1 arevertically disposed in parallel with one another, as shown in FIG. 5. Onthat occasion, every two neighboring capsules, owing to butting of theirspacing protrusions 16--16, leave a space 20 therebetween so that aircan be forcedly circulated through this space.

Within the hollow vessel 10 in the flat PCM capsule 1, each oblongrecess 11 forms a shelf 11' [FIG. 4A], so that the nucleating agent B₂and other additives can deposit on such shelf 11'. As a result,concentrated local accumulation of such additives can be prevented andheat storage can be performed effectively. Furthermore, the presence ofthe holes 13 makes the flow of air complicated and this leads to anincrease in effective heat exchange surface area.

Even when dew condensation occurs on the surface of the PCM capsule 1due to a temperature difference relative to the ambient temperature, thecondensate water is put aside by the air blown under forced circulationin the direction indicated by the arrow x and eventually arrives at thegrooves 15, 15 and flows down therein without difficulty. Similarly,when dew condensation occurs in the recesses 11 and 12, the condensatewater readily flows down the recess inside surface which is slanting,whereby the condensate water retention is effectively inhibited.

FIG. 27 illustrates in section a further example of the heat storagecapsule according to the invention. As shown, this type of capsule 1 hasa hollow doughnut-like configuration, with a through hole 31 passingapproximately the center of a hollow spherical vessel. Said vessel ischarged with the above-mentioned heat storage composition through aninlet 17. The inner and outer wall segments of said doughnut-like hollowvessel serve as heat transfer walls for accumulation or release of heat.Said vessel 1 has a diameter of about 5-20 cm, for instance. A pluralityof capsules of this type are disposed in a heat storage unit and a heatexchange medium is passed through said unit for effecting accumulationor release of heat. In this case, either opening portion of the throughhole 31 of a capsule 1 may be stopped up by a neighboring capsule cominginto close contact therewith and such stoppage may result in decrease inheat accumulation or release efficiency as a result of inhibition of theflow of the heat exchange medium (fluid) through said through hole 31.To avoid such problem, it is desirable to provide, as shown in FIG. 28(cross-sectional view), a plurality of protrusions 32 on the peripheryof each opening portion of the through hole 31 or provide, as shown inFIG. 29, a plurality of grooves 33 on the periphery of each openingportion of the through hole 31 so that even when both the openingportions of the through hole 31 are in contact with neighboring capsules1, openings or spaces can remain for the passage of the heat exchangemedium. The above protrusions 32 or grooves 33 may vary in shape, sizeand other aspects in an optional manner provided that the intention ofsecuring spaces for fluid passage can be accomplished.

When the capsule is in the doughnut-shaped form as shown, the inner faceforming the through hole 31 as well as the outer face of the hollowdoughnut-shaped vessel serves as the heat transfer wall, so that highheat storage-release efficiency can be obtained.

It is desirable to provide such spherical capsule with a plurality ofrib-like protrusions 34 on the inner wall of the heat storagecomposition-receiving room of the hollow spherical vessel 1, for exampleas shown in FIG. 30. Said rib-like protrusions 34 each functions as theabove-mentioned shelf to thereby prevent the localized deposition of thenucleating agent and so on more effectively.

Such hollow spherical vessel can be formed by blow molding or the liketechnique so far known in the art. In molding a hollow spherical vesselhaving rib-shaped protrusions 34 on the inner wall of the heat storagecomposition-receiving room as shown in FIG. 30, it is convenient toproduce intermediate halves 1a and 1b of said vessel, as shown in FIG.31, and then unite said intermediate halves together by adhesion orwelding.

Meanwhile, most generally, the heat storage composition is melted byheating and then introduced in the liquid form into a hollow vessel suchas mentioned above through an inlet 17, which, after charging, istightly stoppered. An advisable stoppering means is as follows: As shownin FIG. 32A and FIG. 32B, which are enlarged cross-sectional partialviews schematically illustrating an example of the means of tightlystoppering the inlet 17, the inlet 17 is formed such that the openingend slightly protrudes and shows a gradual expansion toward theexterior. The stopper 35, which is formed like a wine bottle stopper,preferably, comprises a disk segment 35a and a rod segment 35b formedsolidly with said disk segment 35a and protruding from the middle ofsaid disk segment. (said rod segment being capable of exactly fittingthe above-mentioned inlet 17 and the length of said rod segment 35bbeing almost equal to the depth of the inlet). For fitting and fusiontogether between the inlet 17 and stopper 35, said stopper 35 is pushedinto the inlet 17 while it is rotated at high velocity, as shown in FIG.32A. The portions of the stopper 35 and inlet 17 which are in contactwith each other are welded together as a result of friction heating.After cooling, there can be achieved complete closure of the inlet, asshown in FIG. 32B. Such means of hermetically closing the inlet 17 canbe applied not only to hollow spherical vessels but also to flat vesselssuch as the one shown in FIG. 2 for preventing leakage of the heatstorage composition without fail. As another means of effectingfit-welding, the technique comprising melting the fitting surface ofeach of the inlet 17 and stopper 35 by heating and quickly fitting thestopper into the inlet can also be employed. It goes without saying thatthe means of closure by fusion such as mentioned above is applicable tothose cases in which a thermoplastic material such as a synthetic resinis used as the vessel material.

FIGS. 33A and 33B, which are enlarged partial cross-sectional views,illustrate another fit-fusion technique. The stopper 35 has aring-shaped protrusion 35c on that side of the disk segment 35a whichcarried the rog segment 35b. The fit-fusion welding is conducted in thesame manner as illustrated in FIGS. 32A and 32B. When such means isemployed, the circumferential surface of the rod segment 35b, the lowersurface of the disk segment 35a and the inner circumferential surface ofthe ring-shaped protrusion 35c are all fusion-bonded to the opening wallof the inlet 17, so that an increased sealing length can be attained,hence the sealing effect can be further heightened.

The latent heat storage capsule according to the invention is such aflat or doughnut-shaped capsule as mentioned above with a heat storagecomposition contained therein. Said heat storage composition may be ofany kind. However, a heat storage composition having such a specificcomposition as defined above in accordance with the invention, when usedin combination with a capsule having such geometric characteristics asmentioned above, gives a very good latent heat storage capsule withwhich the excellent heat storage-release characteristics of the heatstorage composition as well as the geometric characteristics of thecapsule body can be exhibited effectively.

A temperature control apparatus in which a plurality of latent heatstorage capsules such as mentioned above are used is now describedtaking as an example the case in which flat PCM capsules are used.

FIGS. 6-8 illustrate an example of the temperature control apparatus inwhich flat PCM capsules with the above-mentioned heat storagecomposition sealed therein are built in. FIG. 6 is a cross-sectionalfront view, FIG. 7 a cross-sectional side view, and FIG. 8 across-sectional view as seen along the line VIII--VIII in FIG. 7. Inthis temperature control apparatus, a heat storage unit 22 comprisesupper and lower rows of flat PCM capsules 1 each containing the heatstorage composition according to the invention. In each row, thecapsules are arranged in the vertical standing position and in parallelwith one another in a holding frame 20, with a space for air passageretained between any two horizontally neighboring capsules. This heatstorage unit 22 and a heating unit 23, which comprises a burning unit23a and a pipe-made heat exchange unit 23b, are built in a hollowhousing 26 provided with an air inlet 24 on the top and four air outlets25 in the lowermost part. A fan-type blower 27 is provided at said airinlet 24 so that air outside the housing can be introduced into thehousing through the air inlet 24 and, after passage through said heatstorage unit 22 and said heating unit 23, sent out of the housing viathe air outlets 25. This temperature control apparatus is placed, asshown in FIG. 9 which illustrates how to use it, within a hothouse 28 orthe like for cultivating various farm products such as tomato an melon,which is a plastic film house or a glasshouse, for instance. The chimney29 of the heating unit 23 is arranged such that it protrudes out of thehothouse 28 for allowing the waste combustion gas to go out of thehouse. In this way, the inside temperature of the hothouse 28 iscontrolled.

Thus, the air within the hothouse is circulated through the inside andoutside of the apparatus housing 26 by means of the blower 27. Duringshining hours, solar energy is supplied to the heat storage unit 22 viathe air within the hothouse and each heat storage capsule 1 absorbs andstores that portion of solar energy which remains after heating of thehothouse to thereby maintain the temperature within the hothouse at anadequate level. After sunset, the air in the hothouse is heated withinthe apparatus 26 by the heat storage capsules 1 so that the hothousetemperature can be maintained at an adequate level. In case heating bythe heat storage unit 22 is insufficient, an oil burner 21 isautomatically or manually actuated so that the hothouse air introducedinto the apparatus 26 can be heated by means of the heating unit 23 tothereby mean the hothouse temperature at an adequate level.

As shown in FIG. 6 and FIG. 7, the above heating unit is disposeddownstream (with respect to the air current caused by the blower 27)from the heat storage unit 22, so that the air heated by the heatingunit 23 will not pass through the heat storage unit 22 or, in otherwords, the air will leave the apparatus 26 without temperature fall dueto heat absorption by the heat storage capsules 1.

In this way, it is now possible to conduct the hothouse heating in caseof insufficient heating by the heat storage unit efficiently with aminimum heat loss in the heat storage unit while suppressing theunevenness in temperature to a possible minimum by means of the blower.In addition, the blower can be used for both heat-storing and heatingpurposes and therefore the apparatus is advantageous from both thestructural and cost viewpoints.

In designing the temperature control apparatus, other constructions thanthat shown in FIGS. 5-8 may also be employed, for example theconstruction shown in FIG. 10 in which the lower set of heat storagecapsules 1 involves only one row or the construction shown in FIG. 11 inwhich the air inlet 24, heat storage unit 22, heating unit 23 and airoutlet 25 are arranged in parallel as viewed in the horizontaldirection.

The following examples of the heat storage composition which is the mostfundamental constituent element in the present invention, together withbackground experimental data which are the bases for establishing therelevant parameters, illustrate the invention in more detail.

EXAMPLES Experiment series 1

The supercooling inhibiting effects of barium sulfide and bariumchloride dihydrate each added alone as a nucleating agent to calciumchloride hexahydrate, as shown Tables 1 and 2, are shown in FIG. 12 andFIG. 13, respectively. In the experiments, 0.001-10 percent of bariumsulfide or barium chloride dihydrate was added to calcium chloridehexahydrate and each heat storage composition was tested for the degreeof supercooling (cf. FIG. 1) by repeating the melting-solidificationcycle.

                  TABLE 1                                                         ______________________________________                                        Some compositions with BaS                                                    as the nucleating agent                                                       Experiment No. BaS (%)  CaCl.sub.2.6H.sub.2 O (%)                             ______________________________________                                        1              0.001    Balance                                               2              0.01     "                                                     3              0.1      "                                                     4              1        "                                                     5              5        "                                                     6              10       "                                                     ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Some compositions with BaCl.sub.2.2H.sub.2 O                                  as the nucleating agent                                                       Experiment No.                                                                             BaCl.sub.2.2H.sub.2 O (%)                                                                  CaCl.sub.2.6H.sub.2 O (%)                           ______________________________________                                        7            0.01         Balance                                             8            0.1          "                                                   9            1            "                                                   10           5            "                                                   11           10           "                                                   ______________________________________                                    

As is apparent from FIG. 12 and FIG. 13, the single use of BaS orBaCl₂.2H₂ O cannot produce a satisfactory supercooling inhibitingeffect. In the above experiments, the nucleating agent contents incomposition No. 6 and No. 11 were too large, namely these compositionsdid not solidify at their respective proper solidification points atall, hence could not be used as heat storage compositions.

In the next place, the supercooling inhibiting effect of the combineduse of barium sulfide and barium chloride dihydrate each in anappropriate amount was examined. Thus, as shown in Table 3, heat storagecompositions were prepared in which the contents of barium sulfide andbarium chloride dihydrate were varied, and they were tested for thedegree of supercooling by repeating the melting-solidification cycle.

                  TABLE 3                                                         ______________________________________                                        Some compositions containing                                                  BaS + BaCl.sub.2.2H.sub.2 O combinedly                                                  BaS      BaCl.sub.2.2H.sub.2 O                                                                      CaCl.sub.2.6H.sub.2 O                         Experiment No.                                                                          (%)      (%)          (%)                                           ______________________________________                                        12        0.0005   0.001        Balance                                       13        0.001                                                               14        0.1                                                                 15        5                                                                   16        10                                                                  17        0.0005   0.05         Balance                                       18        0.001                                                               19        0.1                                                                 20        5                                                                   21        10                                                                  22        0.0005   0.1          Balance                                       23        0.001                                                               24        0.1                                                                 25        5                                                                   26        10                                                                  27        0.0005   5            Balance                                       28        0.001                                                               29        0.1                                                                 30        5                                                                   31        10                                                                  32        0.0005   10           Balance                                       33        0.001                                                               34        0.1                                                                 35        5                                                                   36        10                                                                  ______________________________________                                    

The results obtained are shown in FIGS. 14-18. In the figures, thenumbers correspond to the experiment numbers given in Table 3. Theresults of these experiments suggest:

(1) That when the barium sulfide addition level is less than 0.001percent, the supercooling inhibiting effect is not sufficient even whenthe barium chloride dihydrate addition level is in a proper range andthat, conversely, when the barium sulfide addition level exceeds 5percent, solidification may not take place in some instances (ExperimentNo. 21, No. 26, No. 31 and No. 36) and, even if solidification occurs,the latent heat of solidification becomes reduced and the performance ofthe relevant composition as a heat storage material becomes markedlydecreased.

(2) That when the barium chloride dihydrate addition level is less than0.05 percent, any synergistic supercooling inhibiting effect cannot beproduced in its combined use with barium sulfide, the degree ofsupercooling always exceeding 2°-3° C. That when the barium chloridedihydrate content exceeds 5 percent, solidification does not occur insome cases like in the case of excessive barium sulfide content. It wasfurther confirmed that even when solidification occurs, the latent heatof solidification becomes markedly small.

(3) That, on the contrary, the use of barium sulfide and barium chloridedihydrate each in an adequate amount results in synergistic increase intheir supercooling effect and, as a result, the degree of supercoolingcan be limited to at most 2° C. in any case.

Now, the results of experiments which serve to confirm the effect ofstrontium chloride hexahydrate as the nucleating agent are described.

Heat storage compositions in which the content of strontium chloridehexahydrate was varied as shown in Table 4 were prepared and examinedfor the supercooling inhibiting effect.

                  TABLE 4                                                         ______________________________________                                        Some compositions with SrCl.sub.2.6H.sub.2 O                                  as the nucleating agent                                                       Experiment No.                                                                             SrCl.sub.2.6H.sub.2 O (%)                                                                  CaCl.sub.2.6H.sub.2 O (%)                           ______________________________________                                        37           1.0          Balance                                             38           0.1          "                                                   39           0.05         "                                                   40           0.01         "                                                   41           0.005        "                                                   ______________________________________                                    

As seen from the results shown in FIG. 19, for securing a satisfactorysupercooling effect, strontium chloride hexahydrate must be used in anamount of not less than 0.1 percent.

Example 1

Based on the above experimental results, it was considered that whenstrontium chloride hexahydrate is used combinedly with the above bariumsulfide and/or barium chloride dihydrate, the content of each of thesenucleating agents might be further reduced. Accordingly, thesupercooling inhibiting effect was studied for cases in which thesethree were used combinedly. Thus, heat storage compositions in which thecontents of the above three nucleating agents were varied each in alower addition level range, as shown in Table 5, were prepared andexamined for the supercooling inhibiting effect.

                  TABLE 5                                                         ______________________________________                                        Some compositions containing BaS +                                            BaCl.sub.2.2H.sub.2 O + SrCl.sub.2.6H.sub.2 O combinedly                      Experi-                                                                       ment     BaS     BaCl.sub.2.2H.sub.2 O                                                                    SrCl.sub.2.6H.sub.2 O                                                                 CaCl.sub.2.6H.sub.2 O                     No.      (%)     (%)        (%)     (%)                                       ______________________________________                                        42        0.0001 0.01       0.01    Balance                                   43        0.0001 0.01       0.05    "                                         44       0.001   0.01        0.0005 "                                         45       0.001   0.01        0.001  "                                         46       0.001   0.01       0.01    "                                         47       --      0.5        0.05    "                                         48       --      0.5        0.06    "                                         49       --      0.4        0.06    "                                         50       --      1.0        0.06    "                                         ______________________________________                                    

The result obtained are shown in FIG. 20 and FIG. 21. As is evident fromFIG. 20, the combined use of the above three nucleating agent can reduceto a significant extent the addition levels or contents of therespective agents as required for securing the desired supercoolinginhibiting effect as compared with the single use thereof or thecombined use of two of them. As FIG. 20 indicates, it is advisable thatwhen the amount of strontium chloride hexahydrate is rather small(0.001-0.05 percent), the amount of barium sulfide should be increasedto some extent (not less than 0.001 percent). When strontium chloridedihydrate is used in a relatively large amount (0.01-0.05 percent), asatisfactory supercooling effect can be obtained even at a relativelylow barium sulfide addition level (not less than 0.0001 percent).Furthermore, the data shown in FIG. 21 indicate that when strontiumchloride hexahydrate is used in a relatively large amount (0.06-0.1percent) and barium chloride dihydrate is used combinedly in an amountof not less than 0.5 percent, a satisfactory supercooling inhibitingeffect can be obtained even in the absence of barium sulfide. After all,an excellent supercooling inhibiting effect can be obtained by using thethree nucleating agents in small amounts and adjusting their additionlevels such that the above conditions [I], [II] and [III] are satisfied.

Whereas the synergistic supercooling inhibiting effect producible bybarium sulfide, barium chloride dihydrate and strontium chloridehexahydrate in heat storage compositions whose main component is calciumchloride hexahydrate is as above mentioned, it is usual in practical useof heat storage compositions to further use a thickening agent and/or asolidification point modifier combinedly. Therefore, several typicalexamples of the heat storage composition which contain these additivecomponents are given below, together with the solidification point andthe degree of supercooling (means of 10 repeated cycles) for eachcomposition. As regards the solidification point modifier, detailedmention will be made later in describing a further experiment series.

    ______________________________________                                        (A)     Main component CaCl.sub.2.6H.sub.2 O:                                                                    balance                                            Solidification point                                                                         ZnCl.sub.2 :                                                                              10%                                                modifier                                                                      Nucleating agent                                                                             BaS:        0.0001%                                                           BaCl.sub.2.2H.sub.2 O:                                                                    0.5%                                                              SrCl.sub.2.6H.sub.2 O:                                                                    0.04%                                              Thickening agent                                                                             glycerin:   3%                                         Solidification point:      20° C.                                      Degree of supercooling:    0.7° C.                                     (B)     Main component CaCl.sub.2.6H.sub.2 O:                                                                    balance                                            Solidification point                                                                         NaBr:       10%                                                modifier                                                                      Nucleating agent                                                                             BaS:        0.001%                                                            BaCl.sub.2.2H.sub.2 O:                                                                    0.3%                                                              SrCl.sub.2.6H.sub.2 O:                                                                    0.03%                                              Thickening agent                                                      Ultrafine silica powder:   2.5%                                               Solidification point:      24° C.                                      Degree of supercooling:    1.5° C.                                     (C)     Main component CaCl.sub.2.6H.sub.2 O:                                                                    balance                                            Solidification point                                                                         NH.sub.4 Br:                                                                              12%                                                modifier                                                                      Nucleating agent                                                                             BaS:        0.0001%                                                           BaCl.sub.2.2H.sub.2 O:                                                                    0.05%                                                             SrCl.sub.2.6H.sub.2 O:                                                                    0.04%                                              Thickening agent                                                      Ultrafine silica powder:   2.5%                                               Solidification point       15° C.                                      Degree of supercooling:    1.8° C.                                     (D)     Main component CaCl.sub.2.6H.sub.2 O:                                                                    balance                                            Solidification point                                                                         KBr:        15%                                                modifier                                                                      Nucleating agent                                                                             BaS:        0.1%                                                              CaCl.sub.2.2H.sub.2 O:                                                                    0.05%                                                             SrCl.sub.2.6H.sub.2 O:                                                                    0.04%                                              Thickening agent                                                                             CMC:        4%                                         Solidification point:      18° C.                                      Degree of supercooling:    0.7° C.                                     (E)     Main component CaCl.sub.2.6H.sub.2 O:                                                                    balance                                            Solidification point                                                                         NH.sub.4 Br:                                                                              10%                                                modifier                                                                      Nucleating agent                                                                             BaCl.sub.2.2H.sub.2 O:                                                                    0.65%                                                             SrCl.sub.2.6H.sub.2 O:                                                                    0.07%                                              Thickening agent                                                      Ultrafine silica powder:   2.5%                                               Solidification point:      18° C.                                      Degree of supercooling:    1° C.                                       ______________________________________                                    

Experiment series 2

FIG. 22 is a graphic representation of the tendency toward depression ofthe solidification point of a heat storage composition whose maincomponent is calcium chloride hexahydrate and which contains as asolidification point modifier 5-50 percent of ferric chloridehexahydrate, calcium bromide hexahydrate, potassium bromide, sodiumbromide or ammonium bromide. As is evident from this figure, it ispossible to adjust the solidification point as desired within the rangeof about 30° C. and about 15° C. by using potassium bromide, sodiumbromide or ammonium bromide, selected as a preferred solidificationpoint modifier according to the invention, at an addition level lowerthan the addition levels for the conventional solidification pointmodifiers (e.g. ferric chloride hexahydrate, calcium bromidehexahydrate). As mentioned earlier herein, an increasing amount of asolidification point modifier shows a tendency toward decrease in thequantity of latent heat of the heat storage composition itself, whilethe quantity of latent heat in the use temperature range is essentiallyrequired to be large for a composition to be an excellent heat storagecomposition. However, to lower the solidification point of a eutecticmixture directly leads to a decreased potential energy of the eutecticmixture, so that, essentially, a decrease in the quantity of latent heatcannot be avoided. Thus, the essential problem is by what means thedecrease in the quantity of latent heat which accompanies solidificationpoint depression should be minimized. The above-mentioned bromides aresmaller in the quantity of latent heat as compared with the conventionalsolidification point modifiers, hence can serve to adjust thesolidification point as desired without causing significantdeterioration in the performance of the heat storage composition. FIG.23 shows the change in the quantity of latent heat in a heat storagecomposition, whose main component is calcium chloride hexahydrate, witha varying amount of each of the above three bromides as added to saidcomposition, in comparison with theoretical values calculated on thebasis of the heat of fusion for calcium chloride hexahydrate (45.6cal/g) add with a conventional modifier (zinc chloride). As is evidentfrom FIG. 23, when the above bromides are incorporated, the latent heatvalues differ little from the theoretical values at various additionlevels. On the contrary, in the case of the conventional modifier (zincchloride), the tendency toward decrease in the quantity of latent heatas compared with the theoretical values is remarkable and, when comparedat an equal addition level, the latent heat is much less as comparedwith the bromides. Moreover, the difference therebetween increases withthe increase in the addition level. What has been mentioned above may besummarized in Table 6. Table 6 shows the addition levels required toadjust the solidification point to 20° C. and the latent heat quantitiesat said solidification point for the above bromides and some typicalconventional modifiers (ferric chloride hexahydrate, magnesium chloridehexahydrate and cobalt chloride hexahydrate). As is evident from Table6, potassium bromide, sodium bromide and ammonium bromide can give thedesired solidification point in about one third of the addition levelsrequired for the conventional solidification point modifiers and thelatent heat quantities at said temperature for the bromides are 1.5- to2-fold larger as compared with the conventional compositions. Thus, theuse of at least one of potassium bromide, sodium bromide and ammoniumbromide in accordance with the invention can give a heat storagecomposition having an optionally chosen solidification point with a highlevel of latent heat quantity.

                  TABLE 6                                                         ______________________________________                                                         Addition level                                                                required to                                                                   adjust the                                                                    solidification                                               Solidification   point to 20° C.                                                                     Latent heat                                     point modifier   (%)          cal/g                                           ______________________________________                                        Inven-                                                                              Potassium bromide                                                                             9-12        ca. 41                                      tion  Sodium bromide 10-15        ca. 34                                            Ammonium bromide                                                                              7-10        ca. 40                                      Prior Ferric chloride                                                                              28-30        ca. 23                                      art   hexahydrate                                                                   Magnesium chloride                                                                           30-33        ca. 25                                            hexahydrate                                                                   Cobalt chloride                                                                              32-33        ca. 21                                            hexahydrate                                                             ______________________________________                                    

                  TABLE 7                                                         ______________________________________                                        Composition      (1)      (2)       (3)                                       ______________________________________                                        Basic Calcium chloride                                                                             Balance  Balance Balance                                 compo-                                                                              hexahydrate                                                             sition                                                                              Zinc chloride  12%      12%     12%                                           Disodium hydrogen                                                                            3%       3%      3%                                            phosphate                                                                     Barium sulfide 0.01%    0.0005% 0%                                            Barium chloride                                                                              0.5%     0.5%    0.8%                                          dihydrate                                                                     Strontium chloride                                                                           0.004%   0.04%   0.07%                                         hexahydrate                                                             ______________________________________                                    

The solid line in the figure is for the case in which the ultrafinesilica powder alone was added as the thickening agent, and the brokenline is for the case in which glycerin was added alone. As is evidentfrom FIG. 24, the ultrafine silica powder has excellent thickeningeffect. It gave high viscosity values in lower concentrations ascompared with glycerin, in particular at addition levels not lower than3.5 percent. However, the ultrafine silica powder showed a rapidviscosity increase after the addition level exceeds 3.5 percent. Thismeans that a small difference in addition level means a great variationin viscosity. Such situation is unfavorable from the viscosityadjustment viewpoint and makes it difficult to specify a desiredviscosity particularly in the manufacture of heat storage compositions.

Example 2

FIG. 25 shows the data obtained by adding, to the basic heat storagecomposition (1) given in Table 7, an ultrafine silica powder alone(solid line), the ultrafine silica powder and 1 percent of glycerincombinedly (dot-and-dash line), the ultrafine silica powder and 3percent of glycerin combinedly (dot-dot-dash line) and the ultrafinesilica powder and 5 percent of glycerin (broken line), respectively.Whereas, as mentioned above, the single use of the ultrafine silicapowder at an addition level of about 3.5 percent or above results in arapid viscosity increase, so that fine viscosity adjustment ispractically difficult in said range, FIG. 25 reveals that the use of theultrafine silica powder in combination with glycerin makes gentle theultrafine silica powder content-viscosity curve and furthermore gives anadequate viscosity increase curve also in the addition level range below3.5 percent. Thus, the ultrafine silica powder and glycerin cooperate ina complementary manner across the boundary at the ultrafine silicapowder addition level of about 3.5 percent to give a gentle and adequateviscosity increase curve as a whole. While the pattern of the viscositycurve for the combined use of these two thickening agents is affected ina complicated manner by the addition levels for the respective additivesincluding both the thickeners and other factors, it is advisable andpreferable for adjusting the viscosity of the heat storage compositionto add glycerin in an amount of 1-5 percent and the ultrafine silicapowder in an amount of 1.5-6 percent. By suitably adjusting theproportion between both the thickening agents and the total additionlevel therefor, it is possible to obtain, in heat storage compositions,any desired viscosity within a broad range stably.

Example 3

FIG. 26 shows the stability of a heat storage composition specified inTable 8 as composed of calcium chloride hexahydrate as the maincomponent, a solidification point modifier (zinc chloride) andnucleating agents (barium chloride dihydrate, barium sulfide andstrontium chloride hexahydrate) after addition of (1) an ultrafinesilica powder and glycerin as thickening agents each in an amount of 3percent (solid line), (2) glycerin in an amount of 5 percent(dot-and-dash line) as a thickening agent, or (3) without addition ofany thickening agent. The stability data obtained by repeating themelting-solidification cycle are shown in the figure for comparison.

                  TABLE 8                                                         ______________________________________                                                          Inven-   For com-                                                             tion     parison  Control                                   Composition       (1)      (2)      (3)                                       ______________________________________                                        Calcium chloride hexahydrate                                                                    Balance  Balance  Balance                                   Zinc chloride     12%      12%      12%                                       Barium chloride dihydrate                                                                       0.8%     0.8%     0.8%                                      Barium sulfide    0.01%    0.01%    0.01%                                     Strontium chloride hexahydrate                                                                  0.04%    0.04%    0.04%                                     Glycerin          3%       5%       --                                        Ultrafine silica powder                                                                         3%       --       --                                        ______________________________________                                    

As is evident from FIG. 29, the composition after addition of 3 percenteach of the ultrafine silica powder and glycerin retained a degree ofsupercooling as low as about 1.5° C. even after 300 times of repeateduse, and the increase in the degree of supercooling as observed aftercontinued repeated use was always slight. Even after 700 or more timesof repeated use, the solidification point depression remained not morethan 2.5° C. On the contrary, without the thickening agents, the degreeof supercooling showed a tendency toward rapid increase from thebeginning of repeated use and, after about 100 times of use, said degreereached a level as high as 4.8° C. The composition for comparison(dot-and-dash line) containing 5 percent of glycerin alone retained adegree of supercooling not greater than 2° C. approximately at the 250thcycle. This degree of supercooling, or performance, was comparable tothat found in the case of the combined use of the ultrafine silicapowder and glycerin [composition (1)]. However, after the 250th cycle,the degree of supercooling increased as a result of gradual phaseseparation. Thus it can be understood that the single use of glycerinalone as the thickening agent gives only compositions lacking inlong-term stability in repeated use thereof.

The following are typical examples of the heat storage composition whichcontain an ultrafine silica powder and glycerin as thickening agents andcharacteristics thereof.

    ______________________________________                                        [1]     Calcium chloride hexahydrate                                                                        95%                                                     Strontium chloride hexahydrate                                                                      0.05%                                                   Barium chloride dihydrate                                                                           0.1%                                                    Barium sulfide        0.1%                                                    Ultrafine silica powder                                                                             3.5%                                                    Glycerin              1%                                                      Solidification point 29.6° C.                                          Viscosity 7000 cP                                                     [2]     Calcium chloride hexahydrate                                                                        92%                                                     Strontium chloride hexahydrate                                                                      0.004%                                                  Barium chloride dihydrate                                                                           0.8%                                                    Barium sulfide        0.03%                                                   Glycerin              3%                                                      Ultrafine silica powder                                                                             4%                                                      Solidification point 25° C.                                            Viscosity 4800 cP                                                     [3]     Calcium chloride hexahydrate                                                                        80%                                                     Sodium bromide        15%                                                     Strontium chloride hexahydrate                                                                      0.01%                                                   Barium chloride dihydrate                                                                           0.05%                                                   Barium sulfide        0.01%                                                   Glycerin              3%                                                      Ultrafine silica powder                                                                             4%                                                      Solidification point 19° C.                                            Viscosity 4800 cP                                                     [4]     Calcium chloride hexahydrate                                                                        83.19%                                                  Ammonium bromide      10%                                                     Barium sulfide        0.01%                                                   Barium chloride dihydrate                                                                           0.8%                                                    Strontium chloride hexahydrate                                                                      0.04%                                                   Ultrafine silica powder                                                                             3%                                                      Glycerin              3%                                                      Solidification point 18° C.                                            Viscosity 2500 cP                                                     [5]     Calcium chloride hexahydrate                                                                        Balance                                                 Ammonium bromide      10%                                                     Strontium chloride hexahydrate                                                                      0.07%                                                   Barium chloride dihydrate                                                                           0.65%                                                   Ultrafine silica powder                                                                             5%                                                      Glycerin              3%                                                      Solidification point 18° C.                                            Viscosity 8500 cP                                                     ______________________________________                                    

The present invention has the above-mentioned constitution and theeffects of the invention may be summarized as follows:

(1) The phenomenon of supercooling in heat storage compositions whosemain component is calcium chloride hexahydrate can be radically reducedor substantially prevented by combinedly using barium sulfide, bariumchloride dihydrate and strontium chloride hexahydrate as nucleatingagents each in a small amount in said compositions. Therefore, thetemperature at which the latent heat is utilized can be controlledexactly and precisely without any substantial decrease in heat storagecapacity.

(2) The melt viscosity of such heat storage composition as mentionedabove can be adjusted as desired within a relatively broad range bycombinedly using an ultrafine silica powder and glycerin as thickeningagents each in a small amount. The resulting composition does notdeteriorate with respect to its performance characteristics uponrepeated use thereof.

(3) The improvement in the structure of heat storage capsules mentionedabove which sealedly contain the above heat storage composition furtherensures the dispersion of nucleating agents which serve to promote phasetransition of the heat storage composition and makes it possible for thedew condensate surface water possibly appearing during heat release toflow down easily, so that the heat storage and release effects can beproduced with a maximum efficiency. Each capsule is wholly integralinclusive of recesses as a result of fusion bonding. Furthermore, thegrooves for drainage also serve as reinforcing ribs, so that thestrength of the capsule itself is also improved significantly.

(4) The temperature control apparatus constructed by building the aboveheat storage capsules therein, if in short supply of heat due toinsufficiency of the quantity of heat released by heat storage capsulegroups, can assuredly get supplementary heat supply by means of theheating unit and blower unit and, furthermore, the heat storage andrelease effects of the heat storage capsule groups can be producedefficiently without causing great heat losses.

We claim:
 1. A flat latent heat storage capsule which comprises arectangular plate-like hollow vessel having a plurality of oblongrecesses surrounded by slant faces as formed by bonding together byfusion the face plate bottoms at corresponding sites on both the faceplaces and a plurality of circular holes passing through the hollowvessel in the thickness direction thereof as formed by fusion bonding inthe same manner as above to form circular recesses followed by punchingat least at the fused bottom of said circular recesses and furtherhaving at least one groove-like recess continuously extending in thelongitudinal direction in the neighborhood of each of the left and rightedge portions of each face plate and a protrusion serving as a spacer inthe neighborhood of each of the four corners, the four protrusions oneach face plate being located at sites corresponding to the protrusionson the other face plate, said hollow vessel containing a heat storagecomposition.
 2. A flat latent heat storage capsule which comprises arectangular plate-like hollow vessel having a plurality of oblongrecesses surrounded by slant faces as formed by bonding together byfusion the face plate bottoms at corresponding sites on both the faceplates and a plurality of circular holes passing through the hollowvessel in the thickness direction thereof as formed by fusion bonding inthe same manner as above to form circular recesses followed by punchingat least at the fused bottom of said circular recesses and furtherhaving at least one groove-like recess continuously extending in thelongitudinal direction in the neighborhood of each of the left and rightedge portions of each face plate and a protrusion serving as a spacer inthe neighborhood of each of the four corners, the four protrusions oneach face plate being located at sites corresponding to the protrusionon the other face plate, said hollow vessel containing a heat storagecomposition, which comprises calcium chloride hexahydrate as the maincomponent, which contains, as nucleating agents for preventingsupercooling, 0-5 percent by weight, based on the weight of the totalcomposition, of barium sulfide; 0.001- 5 percent by weight, based on theweight of the total composition of barium chloride dihydrate; and0.001-0.1 percent by weight of strontium chloride hexahydrate, based onthe weight of the total composition.
 3. The flat latent heat storagecapsule of claim 1 or 2, wherein the inlet of the hollow vessel for theheat storage composition is sealed, after charging with saidcomposition, with a stopper by fit-fusion bonding, said stoppercomprising a rod having a length almost equal to the vessel wallthickness at said inlet as measured in the direction of the depth ofsaid inlet.
 4. The flat latent heat storage capsule of claim 1 or 2,wherein the inlet of the hollow vessel for the heat storage compositionis sealed, after charging with said composition, with a stopper byfit-fusion bonding, said stopper comprising a disk segment and a rodsegment formed solidly with said disk segment and having a length almostequal to the vessel wall thickness at said inlet as measured in thedirection of the depth of said inlet.
 5. The flat latent heat storagecapsule of claim 1 or 2, wherein the inlet of the hollow vessel for theheat storage composition is sealed, after charging with saidcomposition, with a stopper by fit-fusion bonding, said stoppercomprising a disk segment and a rod segment formed solidly with saiddisk segment and having a length almost equal to the vessel wallthickness at said inlet as measured in the direction of the depth ofsaid inlet, with a ring-shaped protrusion provided on that side of saiddisk segment which carries said rod segment.
 6. A temperature controlapparatus for use in hothouses or the like which comprises a heatstorage unit equipped with plural units of the flat latent heat storagecapsule of any of claims 1-5, said heat storage unit being built in saidtemperature control apparatus, said temperature control apparatusfurther comprising a blower unit for introducing the air within ahothouse into said apparatus, passing the same through said heat storageunit and sending the same out of said apparatus, said apparatus beingcharacterized in that a heating unit for heating the air introduced intosaid apparatus by said blower unit is built in said apparatus downstream(with respect to the air current caused by said blower unit) from saidheat storage unit.